Day/night sights would typically be used by military and law enforcement personnel to aim weapons used in both day time and night time conditions. Typically, a day/night sight includes an objective lens, a reticle and an eyepiece in series with parallel day and night channels. A channel selector may be used to alternatively direct an image of a target into the day or night channel.
In a day/night sight, the objective lens and the eyepiece may be telescopic to provide a magnified image of the target. The day channel generally uses ambient light to generate an image of the target. The image may be projected to the reticle during day time use to be viewed by the user. The night channel generally includes an image intensifier to generate an illuminated image of the target. The illuminated image may be transmitted to the reticle during night time use to be viewed by the user. The reticle may include markings for aiming the weapon.
A problem with day/night and other types of sights is dust enclosed within the sight. The dust may interfere with the user's view of a scene. This is especially true of telescopic sights that may magnify the dust.